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Biomedical subjects

J W Mitchell

Publications and source records attributed to J W Mitchell.

51 records · Page 3Linked to original sources
PubMed1971

Theoretical and experimental studies of energy exchange from jackrabbit ears and cylindrically shaped appendages.

Convection properties of jackrabbit ears were examined in a wind tunnel and in the field in an attempt to study the possible thermal role of the large ears. This work was part of a study on energy exchange of appendages. Cylindrical copper models of various shapes, aluminum castings of domestic and jackrabbit ears, and an amputated jackrabbit ear were studied in a wind tunnel (a) to define the range for convective heat loss for appendages of various shapes, and (b) to study the effect on convection of model shape and orientation to the wind. Shape, i.e. length and closure, proved important. Orientation to the wind produced no consistent or significant variation in the convection coefficient. The convection coefficients from the ear castings fell within the range generated from the cylindrical models. The convection coefficients for the amputated rabbit ear fell partially within the range. Net thermal radiation loss at midday from the jackrabbit ears was found to be small. Convection from the ears, however, could account for the loss of over 100% of the animal's metabolic heat at an air temperature of 30 degrees C. If air temperature exceeds body temperature, the animal must either store heat or resort to the evaporation of water.

Animals↗
PubMed1968

An analytical model of the counter-current heat exchange phenomena.

An analytical model for the counter-current heat exchange mechanism in animals has been formulated and a solution has been obtained. The nondimensional parameters that govern the mechanism have been determined in terms of the properties of the animal. The normalized temperatures are functions of normalized distance and, in general, three nondimensional heat transfer conductances. Graphical results are presented for two representative physiological systems. These results allow a delineation of those situations in which counter-current heat transfer is important, and also a quantitative prediction of the heat transfer and temperature distributions. The theory is compared to the available experimental results.

Animals↗
PubMed1967

Polar transport related to mobilization of plant constituents.

Indole-3-acetic acid (IAA), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), sucrose, and mannitol, were tested for polar transport through 5-mm hypocotyl segments of bean (Phaseolus vulgaris var. Pinto) seedlings. All 4 compounds were transported in a polar direction. Autoradiographs of segments through which (14)C-labeled compounds were transported indicated areas of (14)C concentration near the morphological base of segments. There was a direct correlation of IAA transport with the ability to initiate roots as well as with the degree of (14)C accumulation in the morphological base of segments. Unlabeled IAA in lanolin applied to segments appeared to reduce transport of IAA-(14)C through those segments when measured by the accumulation of (14)C in a receiver-block of agar, caused an increase in (14)C accumulation in the region to which the unlabeled IAA was applied, and also caused a decrease in accumulation of (14)C at the morphological base of upright segments. Histological studies showed that IAA accelerated cell division and the formation of root primordia particularly at the basal ends, and that these responses sometimes occurred at the expense of cell proliferation at the apical ends of segments. The data presented support the hypothesis that polar movement of IAA, and other endogenous and exogenous substances, in isolated stem segments was controlled by mobilization and utilization of plant constituents at the growth centers.

Journal Article↗